Date of Award

2020-01-01

Degree Name

Master of Science

Department

Geology

Advisor(s)

Hugo A. Gutiérrez-Jurado

Abstract

Plant water use strategies and water transport dynamics are important for understanding ecosystem productivity and soil-vegetation-atmosphere interactions within an environment (Li et al., 2007). Recent research using stable isotope analysis in wet and humid climates has found that vegetation uses tightly particle-bound water stored in the soil that does not participate in translatory flow (Brooks et al., 2010; Goldsmith et al., 2011; McDonnell 2014). In arid and semi-arid deserts of the United States, highly resilient vegetation, such as the Honey Mesquite (Prosopis glandulosa) and the Creosote shrub (Larrea tridentata), exhibit some degree of activity year-round despite limited water availability during the dry season. In an effort to determine the water sourcing strategies of these drought-tolerant species, as well as decern the existence and use of tightly bound soil water in arid and semi-arid environments, we collected and analyzed vegetation stems, soil, and precipitation samples from two sites over a 15-month period in the Jornada Experimental Range (JER) of the Northern Chihuahuan Desert. Using stable isotopes of hydrogen (δ2H) and oxygen (δ18O) we compared the isotopic composition of the mesquite and creosote xylem waters, to that of precipitation and soil water within the two study sites. One site was located in a low-lying channelized area (referred to as the Channel Area) and the other in a slightly higher, flatter area (referred to as the Flat Area). Our results indicate that the location of the vegetation and their associated soil in the landscape has an effect on the isotopic composition of the water they use. The soil water collected from the two study sites exhibited distinctly different behavior-soil water from the Channel Area would become enriched (or depleted) in 18O and 2H faster than the Flat Area. Vegetation stem water samples similarly exhibited different behaviors between the two sites. We found that creosote stem water samples followed the average behavior of the soil water at the site they were located in and they had a larger range of δ18O and δ2H in both sites. This was an indication of their flexibility in arid and semi-arid environments-changing their source to take advantage of available resources (Reynolds et al., 1999; Peters and Gibbens, 2006). Consistent with previous studies, our results also revealed that precipitation and soil water samples from the JER have a seasonal variation in their isotopic composition that is linked to the location that the rainfall event was derived from (Wright et al., 2001; Hu and Dominguez, 2015). Our soil and precipitation samples were isotopically enriched in 18O and 2H during the summer, when rainfall is derived from the Gulf of Mexico, and they were depleted in 18O and 2H during the winter, when rainfall is derived from the Pacific Ocean. Lastly, our results displayed indications of the existence of tightly bound soil water and its possible use by mesquite and creosote within the JER. At the beginning of our study, the soil samples exhibited values that were extremely depleted in 18O and 2H and were not consistent with precipitation samples taken simultaneously. We suggest that a precipitation event with distinct values depleted in 18O and 2H could have occurred prior to our study and were tightly bound within the soil until a subsequent rainfall event. Patterns in the soil and vegetation stem water samples following this event indicate that large precipitation events at the beginning of each the monsoon and dry seasons supply moisture to the soil that is tightly bound and accessible to the vegetation when water is not readily available.

Language

en

Provenance

Received from ProQuest

File Size

71 pages

File Format

application/pdf

Rights Holder

Hayden Eleanor Thompson

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